Endothelial-specific deletion of connexin40 promotes atherosclerosis by increasing CD73-dependent leukocyte adhesion

BACKGROUND

Endothelial dysfunction is the initiating event of atherosclerosis. The expression of connexin40 (Cx40), an endothelial gap junction protein, is decreased during atherogenesis. In the present report, we sought to determine whether Cx40 contributes to the development of the disease.

METHODS AND RESULTS

Mice with ubiquitous deletion of Cx40 are hypertensive, a risk factor for atherosclerosis. Consequently, we generated atherosclerosis-susceptible mice with endothelial-specific deletion of Cx40 (Cx40del mice). Cx40del mice were indeed not hypertensive. The progression of atherosclerosis was increased in Cx40del mice after 5 and 10 weeks of a high-cholesterol diet, and spontaneous lesions were observed in the aortic sinuses of young mice without such a diet. These lesions showed monocyte infiltration into the intima, increased expression of vascular cell adhesion molecule-1, and decreased expression of the ecto-enzyme CD73 in the endothelium. The proinflammatory phenotype of Cx40del mice was confirmed in another model of induced leukocyte recruitment from the lung microcirculation. Endothelial CD73 is known to induce antiadhesion signaling via the production of adenosine. We found that reducing Cx40 expression in vitro with small interfering RNA or antisense decreased CD73 expression and activity and increased leukocyte adhesion to mouse endothelial cells. These effects were reversed by an adenosine receptor agonist.

CONCLUSIONS

Cx40-mediated gap junctional communication contributes to a quiescent nonactivated endothelium by propagating adenosine-evoked antiinflammatory signals between endothelial cells. Alteration in this mechanism by targeting Cx40 promotes leukocyte adhesion to the endothelium, thus accelerating atherosclerosis.

Phorbol ester downregulates PDGFbeta receptor via PKCbeta1 in vascular smooth muscle cells

The role of protein kinase C (PKC) and their isoforms in cell growth regulation remains elusive. Here we showed that in cultured human vascular smooth muscle cells (SMC), the PKC stimulator phorbol 12-myristate 13-acetate (PMA) inhibited [(3)H]thymidine incorporation in response to the growth factor PDGF associated with downregulation of PDGFbeta (but not alpha) receptors, which was recovered to normal level after PKC was depleted. The changes in PDGFbeta receptor were inversely correlated with PKCbeta1 protein levels regulated by PMA. The downregulation of PDGFbeta receptor by PMA was fully prevented by the PKCbeta inhibitor LY379196, however, without recovery of [(3)H]thymidine incorporation to PDGF. In contrast, [(3)H]thymidine incorporation was fully recovered after depletion of PKCs. These results indicate that in human SMC PKCbeta1 mediates PDGFbeta receptor downregulation. Other PKC isoforms activated by phorbol ester also contribute to the inhibitory effects on cell growth.

Chronic vasopeptidase inhibition restores endothelin-converting enzyme activity and normalizes endothelin levels in salt-induced hypertension

BACKGROUND

Vasopeptidase inhibition (VPI) represents a new therapeutic principle including both inhibition of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP). The present study investigated the effect of the vasopeptidase inhibitor omapatrilat on endothelin-1 (ET-1)-mediated vascular function in salt-induced hypertension.

METHODS

Dahl salt-sensitive rats (n=6/group) on standard or salt-enriched (4% NaCl) chow were treated for 8 weeks with either omapatrilat (36+/-4 mg/kg/day), captopril (94+/-2 mg/kg/day) or placebo. Aortic and renal artery segments were isolated and suspended in organ chambers for isometric tension recording. Functional endothelin-converting enzyme (ECE) activity was assessed in native segments and after preincubation with omapatrilat. Furthermore, vascular ECE protein levels as well as plasma and tissue ET-1 levels were determined.

RESULTS

The increase in systolic blood pressure of salt-fed rats was prevented by omapatrilat and captopril to a comparable degree. In salt-induced hypertension, functional ECE activity (calculated as the ratio of the contraction to big ET-1 divided by the contraction to ET-1) in renal arteries (0.46+/-0.05) and in aorta (0.68+/-0.05) was reduced as compared with control animals (0.9+/-0.05 and 0.99+/-0.04, respectively; P<0.05). While omapatrilat in vitro blunted the response to big endothelin-1 (big ET-1) and diminished ECE activity further (P<0.01 vs native segments), chronic treatment with omapatrilat in vivo restored contractions to ET-1 (120+/-6%) and big ET-1 (98+/-9%) in renal arteries, and therefore normalized renovascular ECE activity. In addition, omapatrilat normalized plasma ET-1 concentrations (12.9+/-1.2 vs 16.6+/-1.4 pg/ml on high salt diet; P<0.05) and renovascular ECE protein levels.

CONCLUSIONS

In salt-induced hypertension, vasopeptidase inhibition restores alterations in the endothelin system, such as renovascular ECE activity and responsiveness to ET-1 and big ET-1 with chronic but not acute in vitro application. Thus, the beneficial effects of vasopeptidase inhibition may reflect a resetting of cardiovascular control systems and therefore may be particularly suited to treat hypertension and heart failure.

HMG-CoA reductase inhibition improves endothelial cell function and inhibits smooth muscle cell proliferation in human saphenous veins

OBJECTIVES

This study examined effects of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase inhibitor cerivastatin on human saphenous vein (SV), endothelial cells (EC) and smooth muscle cells (SMC).

BACKGROUND

Venous bypass graft failure involves EC dysfunction and SMC proliferation. Substances that improve EC function and inhibit SMC proliferation would be of clinical relevance.

METHODS

Both EC and SMC were isolated from SV. Endothelial nitric oxide synthase (eNOS) expression and nitric oxide (NO) production were analyzed by immunoblotting and porphyrinic microsensor. The SMC proliferation was assayed by 3H-thymidine incorporation. Protein kinases and cell cycle regulators were analyzed by immunoblotting.

RESULTS

Cerivastatin (10(-9) to 10(-6) mol/liter) enhanced eNOS protein expression and NO release (about two-fold) in EC in response to Ca2+ ionophore (10(-6) mol/liter). This was fully abrogated by the HMG-CoA product mevanolate (2 x 10(-4) mol/liter). In SMC, platelet-derived growth factor (5 ng/ml) enhanced 3H-thymidine incorporation (298 +/- 23%, n = 4), activated cyclin-dependent kinase (Cdk2), phosphorylated Rb and down-regulated p27Kip1 (but not p21CiP1). Cerivastatin reduced the 3H-thymidine incorporation (164 +/- 11%, p < 0.01), inhibited Cdk2 activation and Rb phosphorylation, but did not prevent p27Kip1 down-regulation, nor p42mapk and p70S6K activation. Mevalonate abrogated the effects of cerivastatin on Cdk2 and Rb but only partially rescued the 3H-thymidine incorporation (from 164 +/- 11% to 211 +/- 13%, n = 4, p < 0.01).

CONCLUSIONS

In humans, SVEC inhibition of HMG-CoA/mevalonate pathway contributes to the enhanced eNOS expression and NO release by cerivastatin, whereas in SMC, inhibition of this pathway only partially explains cerivastatin-induced cell growth arrest. Inhibition of mechanisms other than p42mapk and p70S6K or Cdk2 are also involved. These effects of cerivastatin could be important in treating venous bypass graft disease.